Fluid analyzing systems



June 13,1967 l E. L. SZONNTAGH 3,324,709

FLUID ANALYZING SYSTEMS Filed Sept. 5, 1963 United States' Patent 3,324,709 FLUID ANALYZING SYSTEMS Eugene L. Szonntagh, Flourtown, Pa, assignor to Leeds & N orthrnp Company, a corporation of Pennsylvania Filed Sept. 3, 1963, Ser. No. 306,236 6 (Ilaims. (Cl. 733-231) This invention relates to fluid analyzers, particularly of the chromatographic type and has for an object the provision of a reliable chromatograph analyzer adapted for the measurement of mixtures of gases which may be separated in chromatographic columns during widely differing retention times therein.

Os well understood by those skilled in the art, in gas chromatography a gas sample is caused to flow through a column generally in the form of a tube packed with a suitable material such for example as charcoal, ground fire brick impregnated with selected liquids, and frequently including a molecular sieve. For lower boiling point materials, as fixed gases, the retention time within a column is relatively shorter. Accordingly, if a fluid to be analyzed contains a mixture of low boiling and high boiling gases, it will be understood at once that a column which effectively separates the low boiling materials will retain therein higher boiling materials for a longer time than is necessary for the determination of their concentration in the mixture. Accordingly, it has been proposed to utilize two columns, one designed for the higher boiling point materials and the other designed for the lower boiling point materials. When the measurement is being made of the high boiling materials, a dummy column is connected for flow of the carrier-sample stream in place of the column designed for the low boiling materials.

Inasmuch as a bridge network is normally used in determinating the concentration of the constituents in the sample stream, it will be understood at once that when the sample stream is connected for flow through the dummy column any change in rate of flow by reason of a flow resistance differing from that of the column it has replaced will cause a variation in the output of the bridge.

In accordance with the present invention there is provided for the measuring network, zero adjusting means preferably in the form of multi-turn potentiometers each of which may be adjusted to change the output of the bridge. Thus, if there be established a flow of carrier gas through the two columns in series, one potentiometer can be adjusted to zero the bridge for that given rate of flow. By suitable actuation of valves, the flow of carrier gas may then be established through but one column and through the dummy column and thence through the measuring cell. At the same time a switch connects the output of the bridge to the second potentiometer which is again utilized to balance the bridge. The two potentiometers are geared together and the drives thereto include at least one slip clutch so that thereafter both potentiometers may, through a suitable zero adjusting motor and a slip clutch, be driven together. This means that after the bridge has been adjusted for a proper zero for each of the two alternate flow paths, any change in the over-all rate of flow or any changes otherwise affecting the measurements with either of the two alternate rates of flow Will cause the zero-adjusting motor concurrently to drive the two potentiometers maintaining their relative displacements one to the other. In this manner there will be maintained zero balance for the bridge in the absence of a sample in mixture with the carrier gas flowing therethrough.

For further objects and advantages of the invention and for examples of typical apparatus for achieving the same, reference is to be had to the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. 1 diagrammatically illustrates a chromatograph and associated network to which the invention has been applied;

FIG. 2 diagrammatically illustrates the structural relationship of the two potentiometers illustrated in FIG. 1; and

FIG. 3 is a plan view, partly in section, of a preferred embodiment of the invention.

Referring now to FIG. 1, there has been illustrated a bridge 10 including resistors R and R in adjacent arms thereof and also a resistor R disposed between them. In the third and fourth arms of the bridge there are disposed a reference cell T and a measuring cell T These may be. of the conventional thermistor type. As well understood by those skilled in the art a carrier gas is normally caused to flow through the reference cell T as by way of an inlet 11 and thence through a sampling valve 12. This sampling valve 12 may take various forms known to those skilled to the art and preferably is of the type shown in my application Ser. No. 150,783, filed Nov. 7, 1961, Patent No. 3,205,701. In brief, the carrier gas as shown has a path directly through the valve. It passes from valve 12 by way of a flow connection 13 to a chromatographic column C which includes a packing particularly suitable for gases with relatively higher boiling points, like hydrocarbons. The carrier gas flows through this column C and by way of a three-way valve 14 through a second chromatographic column C This column will have a packing particularly suited to low boiling point gases. The carrier gas flows from column C through a second three-way valve 15 and thence through the measuring cell T The bridge 10 in energized from any suitable source of supply indicated as direct current by the conventional symbols. The output of the bridge is applied to output terminals and connected to a suitable measuring device indicated as To Recorder. One output connection 16 from the bridge 10 extends to the junction between reference cell T and measuring cell T The other output connection from the bridge extends by way of conductor 17 and a single pole double throw switch 18 to one or the other of a pair of adjustable contacts 1% and 20a of potentiometers P and P 'I' hese potentiometers are connected in shunt across the resistor R3 which extends between resistors R and R of the bridge 10*.

With carrier gas only flowing through the columns C and C and through the cells T and T it will be seen that the bridge 10 may be balanced by relatively adjusting the contact 19a of the multi-turn resistor or potentiometer P This contact 19a is adjusted to a position which balances the bridge.

Assuming now that the valves 14 and 15 have been operated to direct the flow of the carrier gas through the dummy column C and at the same time transferring the connection of the switch 18 to the potentiometer contact 20a of potentiometer P it will be seen that the bridge 10 may or may not be in balance. If the flow rate through the dummy'column C differs from that through the column C then the bridge will be unbalanced. However, by adjusting contact 20a in the proper direction, the bridge 10 will again be in balance.

During the operation of the system as a whole, changes may take place in the flow rate, aging can take place in the columns, and other factors may affect bridge balance. Accordingly, it is desirable in the operation of chromatographic systerns occasionally to recalibrate the measuring network and to compensate for drift of the base line i.e., to correct for variations in zero output at the time that carrier gas alone is passing through the reference cell T and the measuring cell T In order that the adjustment of both potentiometers will not disturb the individual adjustments made as described above, the potentiometers P and P are, in accordance with the present invention, interconnected by gears G and G In the driving connection from gear G to potentiometer P there is disposed a slip clutch K By reason of this slip clutch, it will be seen that a knob D may be rotated relatively to change the position of contact 2811 of potentiometer P without changing the adjustment of the potentiometer P That potentiometer can be held stationary by reason of the connection of its shaft to a gear G which through a gear G and a slip clutch K is connected to the zero adjusting motor M. The forgoing independenoe of adjustment is made possible, of course, by having the opposition to movement of slip clutch K less than that of slip clutch K If it be desired to adjust potentiometer P independently of potentiometer P then the knob D may be held stationary and knob D rotated to change the position of contact 19a on the resistor P the rotation occunring by reason of the slippage at both of clutches K and K From the foregoing, it will be seen that contacts 19a and 20a may be moved to any desired positions on their respective resistors P and P in order to accommodate the adjustments required for zeroing the output of the bridge under the many varied conditions of operation encountered.

In order that the base line may be adjusted i.e., maintained at a predetermined level, a zero adjusting network 21 is provided which energizes the motor M to drive through the slip clutch K and the gears G G and G the two potentiometers P and P concurrently to move them with their contacts displaced for the individual ad justments as described above. Thus, while the level of output of the bridge 10 is changed by operation of motor M, the differential in the adjustments between contacts 19a and 20a is not disturbed.

It is to be observed that when the motor M drives gear G it rotates gear G in one direction and the gear G in the opposite direction. Accordingly, it will be understood that the multi-turn resistor of one of the potentiometers will be connected oppositely to the other so that the electrical change made by the concurrent rotation of the contacts of the two potentiometers in opposite directions will make electrical changes in the same direction. In the preferred form of the invention, the potentiometers P and P are preferably of the type available on the market under the trade name Helipot. These devices are made so that either the contact is rotatable or the multi-turn resistor is rotatable relative to a stationary contact. In the present description it has been convenient to refer to the contact as being adjustable, it being understood that this terminology embraces either arrangement.

Normally in the adjustment of the potentiometers P and P and as indicated by the drawing, the potentiometer P first will be adjusted to produce zero output for the bridge 10. This adjustment will, through the gear G and clutch K change the position of contact 20a of potentiometer P After the switch 18 has been moved to its right-hand position, the potentiometer P will then be adjusted to take care of any variations including that due to the dummy column C At this time the clutch K of less opposition to rotation than the clutch K permits the adjustment to take place without driving gears G and G Thus, in normal operation it will be unnecessary to hold one knob while the other is rotated.

In connection with the zero adjusting network 21 and the sample-injecting valve 12, reference may be had to my aforesaid copending application Ser. No. 150,783, Patent No. 3,205,701, for a more detailed disclosure of suitable programming and driving mechanisms therefor. In brief, the sample-injecting valve 12 is rotated at substantially constant speed periodically to transfer the illustrated connection for flow of carrier gas through one or the other of the columns to a position in communication with an inlet 22 for the sample of gas to be analyzed.

When the sample-containing chamber 12a receives gas from inlet 22 and discharges the same from an outlet 23, the carrier gas continues to flow through the system. After a predetermined volume of gas has been introduced into the sampling chamber 12a, that volume is then transferred to the system, the chamber then being in the position illustrated for flow of that sample by means of and in mixture with the carrier gas first through column C and then through column C With the parts in the illustrated position, it can be assumed that the constituents to be measured are of the fixed gas group and hence, there will be required the column C packed with materials particularly suited for fixed gases and including for example, a molecular sieve or other adsorption columns particularly suited for these constituents. The bridge 10 then responds as each of the gaseous constituents appears at the measuring cell T and their peak values are recorded in well understood manner.

When the sample stream 22 includes constituents which do not require the time of the fixed gases in the columns for elution thereof, then the valves 14 and 15 are operated by the program controller, or manually if desired, to transfer the flow through the dummy column C In this operation, the column C performs the separating functions of the constituents which in turn are meas ured as they pass through the measuring cell T In this connection it will be noted that the valves 14 and 15 isolate the column C from the flow and diffusion therein of gases when the bypass through the dummy column has been completed.

In the above description, reference has been made to low boiling and high boiling constituents and also to fixed gases and to hydrocarbons. It is to be understood that the reference to low boiling and high boiling constituents is a relative matter. Thus, fixed gases, in general, are low boiling and hydrocarbons above about C can be classed as higher boiling point materials. Methane may be classed as a low boiling material. Thus, it has been demonstrated that for various mixtures the columns C, C and the by pass column C will be utilized depending upon the na-- ture in character of the constituents to be measured. In addition to minimizing the retention time due to column C and to achieve rapid measurements of the higher boil ing point materials by use of the bypass through dummy column C, the arrangement also lends itself to protection of the column C from contamination when gases of a type which may contaminate the packing in the column appear in the sample to be analyzed.

Referring now to the preferred embodiment of FIG. 31 corresponding parts have been given the same reference characters as in FIGS. 1 and 2. Thus, the potentiometers P and P mounted from a panel 24 can be adjusted by their respective knobs D and D The potentiometers P and P are rotated in the same direction for a corresponding change in electrical resistance thereof in contrast with the opposite rotations in the embodiment of FIG. 2. Thus, the motor M drives the intermediate gear G; by way of a friction clutch corresponding with the clutch K of FIG. 2. This clutch, in FIG. 3, comprises a spring 30 which by means of the two lock nuts 31 presses against a washer 32. Thus, the gear G is pressed against a corresponding washer 33 disposed between the gear and the hub of a bushing 34 secured by a set screw 35 to the motor shaft. The frictional drive is readily adjustable by changing the spring-force applied to the driving washers.

The potentiometer P has its shaft 36 extending through the gear G and its end-portion has secured to it a bushing 37 as by a set screw 38. By means of lock nuts 39, a spring 40 is placed under compression and through washer 41 presses the gear G against the washer 42 and the hub of bushing 37 to provide a friction drive between the the gear G and the shaft 36. As in the modification of FIG. 2 the lock nuts 31 will be tightened to a greater extent than the lock nuts 39 or different size springs utilized to assure a greater driving effort through the clutch as-' sociated with the motor shaft than the clutch associated with the shaft 36 of potentiometer P It is believed that the description of FIG. 2 will be adequate for an understanding of the operation of the preferred embodiment of FIG. 3. In brief, the knob D will be rotated with the parts in their illustrated positions in FIG. 1 to provide the desired zero output on the measuring bridge Thereafter, the valves 14 and 15 will be operated concurrently with operation of switch 18 to connect into the output circuit the potentiometer P This potentiometer through knob D will then be adjusted to a position independent of the position of P The clutch associated with the motor shaft holds gear G stationary and so prevents transmission of torque by way of gear G to gear G As in the case of the embodiment of FIG. 2 subsequent energization of the motor M will rotate the two potentiometers P and P in the same direction concurrently to adjust the output of the bridge in compensation for changes in flow rate and other factors discussed at length above.

Now that preferred embodiments of the invention have been described, it will be understood that other changes may be made within the scope of the appended claims.

What is claimed is:

1. The combination with a fluid analyzer having alternative paths for the flow of fluid to be analyzed first through one and then through another of said paths, of an electrical measuring network including a measuring cell which is in a flow path common to said alternate paths and responsive to change in the rate of flow of fluid therethrough and to a change of constituent concentration of the fluid passing therethrough for unbalancing said network,

switch means,

a potentiometer for each of said flow paths, one potentiometer being connectable in said network by said switch means for balancing said network with said fluid passing through one of said paths and another potentiometer being connectable in said network by said switch means for balancing said network with fluid passing through another of said paths,

means for independently adjusting each of said potentiometers relative to the other to produce balance of said network with said flow of fluid first through one and then through another of said paths, and

driving means for thereafter driving all of said potentiometers in directions to change the balance of said network in the same direction.

2. The combination with a fluid analyzer having a common flow path branching into alternate paths for the flow of fluid to be analyzed first through one and then through another of said alternate paths, of a balanceable measuring network including circuit components at least one of which is located in said common flow path and responsive to a change of constituent concentration of the fluid passing therethrough for unbalancing said network, and is likewise responsive to any change in the rate of fluid flow therethrough as a result of any difference in the resistance to fluid flow in said alternate paths to also unbalance said network,

electrical switch means in said network,

first adjustable impedance means electrically connectable by said switch means in said network and having a first element adjustable to balance said network when fluid flow is through a first of said alternate paths during the absence of change in said constituent concentration,

second adjustable impedance means electrically connectable by said switch means in said network as a substitute for said first adjustable impedance means, said second adjustable impedance means including a second element independently adjustable to balance said network when fluid flow is through a second of said alternate paths and during the absence of change of said constituent concentration, and

driving means responsive to an output from said electrical network by way of a common connection therewith and either of said first or second elements for concurrently moving both said first and second elements automatically in directions to change the balance of said network in the same direction irregardless of the flow of fluid through either of said alternate paths.

3. The combination with a fluid analyzer having alternate paths for the flow of fluid to be analyzed first through one and then through another of said paths, of a balanceable electrical measuring network including components in circuit with said network, at least one of which is associated with and responsive to a change of constituent concentration of the fluid passing therethrough for unbalancing said network,

potentiometer means for each of said alternate paths connected to said network for balancing said network first with said fluid passing through one of said paths and then with fluid passing through another of said paths,

means for independently adjusting each of said means relative to the other to produce balance of said network with said flow of fluid first through one and then through another of said paths, and

driving means for thereafter driving all of said means in directions to change the balance of said network in the same direction.

4. The combination with a chromatograph having at least three columns, one being a dummy column and valve means for selectively establishing flow of fluid through one column and selectively through either said dummy column or a second of said columns, of a measuring system of the bridge type including a reference cell in one arm thereof for flow of carrier gas therethrough,

a measuring cell in another arm of said system for the flow of said fluid therethrough and for unbalancing said system in response to change of concentration of constituent levels in said fluid, and change in the rate of flow of said fluid as a result of difference in the resistance to fluid flow through said dummy and said second of said columns,

a first potentiometer in circuit with said system for balancing said system when flow of fluid is through said dummy column and a second potentiometer for balancing said system when flow of fluid is through said second of said columns,

driving gears interconnecting said potentiometers for concurrent adjustment thereof,

at least one slip clutch disposed between one of said potentiometers and its driving gear whereby each potentiometer may be adjusted relative to the other for establishing different balance conditions of said system in compensation for different flow conditions through said measuring cell,

a zero adjusting drive motor operable upon unbalance of said system for driving said gears, to concurrently adjust said potentiometers to reestablish balance of said system regardless of flow of fluid through said dummy or said second of said columns, and

a slip clutch disposed between said motor and its connecton to said gears for permitting adjustment of one or both of said potentiometers with said motor at standstill.

5. The combination of claim 4 in which said valve means are operable between first and second positions for establishing flow of fluid selectively through said second of said columns and said dummy column,

a single pole double throw switch in the output of said measuring system for establishing connections to one or the other of said first and second potentiometers, and

means coordinating the operation of said switch with the operation of said valve means for maintaining the balance of the system corresponding with the flow of fiuid through either said dummy column or through said second of said columns.

6. The combination with a chromatograph having at least one column within which elution of constituents of a fluid may take place, of at least one alternative flow path for said fluid having a flow resistance comparable to the flow resistance through said column,

valve means for selectively establishing flow of fluid through said one column and through one of said alternative paths,

a measuring system of the bridge type including a reference cell in one arm thereof for flow of carrier gas therethrough,

a measuring cell in another arm of said system for flow of fluid therethrough for unbalancing said system in response to change of concentration of conconstituent levels in said fluid, and change in the rate of flow of said fluid as a result of difference in the resistance to flow through said alternative paths,

two potentiometers connected in parallel one to another across the remaining arms of said bridge,

driving gears interconnecting said potentiometers for concurrent adjustment thereof,

at least one slip clutch disposed between one of said potentiometers and its driving gear whereby each p0 tentiometer may be adjusted relative to the other for establishing different balance conditions of said system in compensation for diiferent flow conditions through said measuring cell,

a zero adjusting drive motor operable upon unbalance of said system for driving said gears to rebalance said system, and

a slip clutch disposed between said motor and its connection to said gears for permitting adjustment of one or both of said otentiometers with said motor at standstill.

References Cited UNITED STATES PATENTS RICHARD C. QUEISSER, Primary Examiner.

7/1964 Russell 338131 X 

1. THE COMBINATION WITH A FLUID ANALYZER HAVING ALTERNATIVE PATHS FOR THE FLOW OF FLUID TO BE ANALYZED FIRST THROUGH ONE AND THEN THROUGH ANOTHER OF SAID PATHS, OF AN ELECTRICAL MEASURING NETWORK INCLUDING A MEASURING CELL WHICH IS IN A FLOW PATH COMMON TO SAID ALTERNATE PATHS AND RESPONSIVE TO CHANGE IN THE RATE OF FLOW OF FLUID THERETHROUGH AND TO A CHANGE OF CONSTITUENT CONCENTRATION OF THE FLUID PASSING THERETHROUGH FOR UNBALANCING SAID NETWORK, SWITCH MEANS, A POTENTIOMETER FOR EACH OF SAID FLOW PATHS, ONE POTENTIOMETER BEING CONNECTABLE IN SAID NETWORK BY SAID SWITCH MEANS FOR BALANCING SAID NETWORK WITH SAID FLUID PASSING THROUGH ONE OF SAID PATHS AND ANOTHER POTENTIOMETER BEING CONNECTABLE IN SAID NETWORK BY SAID SWITCH MEANS FOR BALANCING SAID NETWORK WITH FLUID PASSING THROUGH ANOTHER OF SAID PATHS, MEANS FOR INDEPENDENTLY ADJUSTING EACH OF SAID POTENTIOMETERS RELATIVE TO THE OTHER TO PRODUCE BALANCE OF SAID NETWORK WITH SAID FLOW OF FLUID THROUGH ONE AND THEN THROUGH ANOTHER OF SAID PATHS, AND DRIVING MEANS FOR THEREAFTER DRIVING ALL OF SAID POTENTIOMETERS IN DIRECTIONS TO CHANGE THE BALANCE OF SAID NETWORK IN THE SAME DIRECTION. 